Oh hello there, it’s nice for you to contact me about it. And your concept sounds interesting and I’ll be sure to see how it goes ^^
Anyway, my enlarging actually isn’t any huge clean up process. I actually just zoom up sprites and then use the Print Screen tool to have them enlarged without the blurriness of making them bigger through the transform tool. The normal is 200%, while others that have Twilight closer up like my last Twibrary update is done was zoomed in at 500%
However I recommend that you first make the poses you want to make at normal size and then use zoom and Print Screen because otherwise a twice as large sprite might be a little harder to edit then it should be.
Though if you have any special effects (Like the horn glow), that’s best to save for the enlarged sprites.
I hope that’s helpful enough, if not… feel free to ask me more questions.
(P.S. I don’t know what program you use or if my method works better for my own then others. But I use Photoshop to make mine. Not 100% sure if it works as good if you use say… GIMP, Paint, or SAI)